I was searching for a way to read data from a 3.5mm hack using an Arduino, but I couldn't find a well-detailed, beginner-friendly, tutorial on how to make this, at least how to wire everything and create a simple I/O code. Anyone know a good, beginner-friendly, tutorial about this topic?

PS: I don't want to use a modem like this, I to learn and make it not communicate only with iOS/Android devices.